This invention relates generally to data storage systems and more particularly to data storage systems having a plurality of magnetic storage disk drives in a redundancy arrangement whereby the disk drives are controllable by first disk controllers and second disk controllers. Still more particularly, the invention also relates to systems of such type wherein the disk drives are coupled to the disk controllers through a series, unidirectional, xe2x80x9cringxe2x80x9d or, fiber channel protocol, communication system.
As is known in the art, in one type of data storage system, data is stored in a bank of magnetic storage disk drives. The disk drives, and their coupled interfaces, are arranged in sets, each set being controlled by a first disk controller and a second disk controller. More particularly, in order to enable the set of disk drives to operate in the event that there is a failure of the first disk controller, each set is also coupled to a second, or redundant disk controller. Therefore, if either the first or second disk controller fails, the set of disk drives is accessible by the other one of the disk controllers.
While today most disk storage systems of this type use a Small Computer System Interconnection (SCSI) protocol, in order to operate with higher data rates, other protocols are being introduced. One higher data rate protocol is sometimes referred to as a fibre channel (FC) protocol. Such FC channel protocol uses a series, unidirectional, xe2x80x9cringxe2x80x9d communication system. In order to provide for redundancy, that is, to enable use of the set of disk drives in the event that the first disk controller fails, as discussed above, the set is coupled to the second, or redundant disk controller, using a separate, independent, xe2x80x9cringxe2x80x9d, or fibre channel communication protocol. Thus, two fibre channels are provided for each set of disk drives and their disk interfaces; a first fibre channel and a second fibre channel.
As is also known, when using the fibre channel communication protocol, if any element in the channel becomes inoperative, the entire channel becomes inoperative. That is, if the first disk controller becomes inoperative, or if any one of the disk drives in the set coupled to the first channel becomes inoperative (i.e., as where the disk interface fails, the disk interface is inoperative, or removed with its coupled disk drive, or where the disk drive coupled thereto fails, or is removed), the first fibre channel, is xe2x80x9cbrokenxe2x80x9d, or open, and becomes inoperative. The data stored in the entire portion of the set of disk drives coupled to the first disk channel is therefore unavailable until the inoperative first disk controller or inoperative disk drive is replaced. This is true with either the first channel or the second channel. One technique suggested to solve this problem is through the use of a switch, sometimes referred to as an LRC (i.e., a loop resiliency circuit) switch. Such LRC switch is used to remove an inoperative disk drive from its channel.
In one suggested arrangement, a printed circuit board is provided for each disk drive. The printed circuit board has a pair of LRCs, one for the first channel and one for the second channel. Thus, the open channel may be xe2x80x9cclosedxe2x80x9d in the event of an inoperative disk drive by placing the LRC thereof in a by-pass condition. While such suggested technique solves the inoperative disk drive, or open channel problem, if one of the pair of LRCs fails, the entire printed circuit board having the pair of LRCs must be replaced thereby disrupting both the first and second channels; and, hence, disrupting the operation of the entire data storage system.
One technique suggested to solve this disruption problem requires n LRC switches (where n is the number of disk drives in the set) in the first channel, i.e., one LRC for each one the n disk drives in the set and another n LRC switches in the second channel for each one of the n disk drives in the second channel. The first channel set of n LRCs is mounted on one printed circuit board and the second channel set of n LRCs is mounted on a different printed circuit board. A backplane is used to interconnect the two LRC printed circuit boards, the associated selectors, or multiplexers, and the disk drives. In order to provide the requisite serial, or sequential, fibre channel connections, an elaborate, complex, fan-out wiring arrangement has been suggested for the backplane. Further, the slots provided for the two LRC boards eliminates two disk drives, and the disk interfaces which would otherwise be plugged into these two slots of the backplane.
Another fibre channel arrangement is described in U. S. Pat. No. 5,729,763 entitled xe2x80x9cData Storage Systemxe2x80x9d, inventor Eli Leshem, issued Mar. 17, 1998, assigned to the same assignee as the present invention.
In accordance with the present invention, a data storage system is provided wherein a host computer is coupled to a bank of disk drives through a system interface. The interface includes a plurality of directors and a memory interconnected by a plurality of busses for controlling data transfer between the host computer and the bank of disk drives as such data passes through the memory. A front-end portion of the directors is coupled to the host computer through front-end input/output adapters. Each one of the front-end directors includes a fibre channel hub. The hub is configured to provide a selected one of a plurality of fibre channel loops between one of the front-end directors and a selected one, or more, of a plurality of host computer sections. The fibre channel hub includes a plurality of transceivers each one being adapted to communicate with a corresponding one of the plurality of host computer sections. A plurality of multiplexer sections is coupled to a said one of the directors through a configurable fibre channel loop. Each one of such multiplexer sections is coupled to a corresponding one of the plurality of host computer sections through a corresponding one of the transceivers. Each one of the multiplexer sections is responsive to control signal for coupling, or decoupling, the one of the host computer sections coupled thereto to, or from, the loop selectively in accordance with the control signal.
In accordance with another aspect of the invention, each one of the multiplexer sections comprises: an input port; an output port; and a multiplexer. The multiplexer has a pair of input ports and an output port, such output port being coupled to the output port of the multiplexer section. The input port to the multiplexer section is coupled directly to a first one of the pair of input ports of the multiplexer through a first fibre channel path and is coupled to a second one of the pair of input ports of the multiplexer though the one of the transceivers coupled thereto through a second fibre channel path.
In accordance with one embodiment of the invention, the second fibre channel path includes: a transmit re-timer between the input of the multiplexer section and an input to the transceiver; and, a receive re-timer between an output of the transceiver and the second input of the multiplexer section.